Control circuit for character display tube



June 2, 1959 Filed- Dec. '29, 1954 Fig; 1

STEP AND RESET PULSES MAGNETIC STORAGE DEVICE 2 Sheets-Sheet 1 STEP AND RESET PULSES CHARACTER CHARACTER SELECTOR AND AMPLIFIER HORIZONTAL FORMAT GENERATOR HORIZONTAL POSITION SELECTOR AND AMPLIFIER VERTICAL I FORMAT GENERATOR VERTICAL POSITION AMPLIFIER AMPLIFIER INVENTOR.

C. A. WESLEY ATTORN EY c. A. WESLE'Y June 2, 1959 CONTROL CIRCUIT FOR CHARACTER DISPLAY TUBE Filed Dec. 29, 1954 2 Sheets-Sheet 2 Fig. E

SELEC'UON AMPLIFIER LEAD 2| LEAD 22 if LEAD 23 VERTICAL POSITION AMPLIFIER FORMAT m A L T CAA R N R Mm... T s m s 6 Fig. 5

Z" 4 .u w IL M L T A m N E G R mm m s c INVENTOR.

C. A. WESLEY ATTORNEY United States CONTROL CIRCUIT FOR CHARACTER DISPLAY TUBE Application December 29, 1954, Serial No. 478,459

4 Claims. (Cl. 340-324) The present invention relates generally to a system for registering or posting information for visual observation. Information that may be represented by characters such as letters or numerals may be conveniently displayed by character-forming cathode ray tubes which are well known and commercially available. Examples of such tubes are the Typotron and Charactron, manufactured by Hughes Aircraft Company and Consolidated Vultee Company, respectively. For a detailed description of this type of tube reference may be had to the publication of the Research and Development Laboratories of Hughes Aircraft Company, Culver City, California, dated April 5, 1954, and entitled The Typotron. Information from a storage device or other source may be fed to one of these tubes in the form of binary signals which are first translated into proper control potentials.

More specifically, this invention is directed to the control circuits for deriving the control potentials from received binary signals. Systems in current use for effecting character selection are generally controlled by binary signals on three leads. These signals are passed to a code translator which gates on a channel determined by the incoming code. Each channel corresponds to a given row in the character-forming matrix of the display tube. This tube will be described in detail hereinafter. The output voltage of each channel is adjustable and all the outputs are brought to a common junction point. The potential of this point at any given instant therefore depends; upon the incoming binary signals and the adjusted voltage of the selected channel. The voltage adjustment is performed for proper selection of the required row. A corresponding arrangement is used for selection of columns of the character matrix.

This former system of character selection requires a complex circuit including a large number of diodes and vacuum tubes and is therefore expensive, cumbersome and subject to malfunction. For example, the character selector formerly used consists of diode matrices and phase inverters properly interconnected. Following the ggoups; of' matrices for horizontal selection of columns it;was necessary to have two, triodes for eachmatrix, one ofwhich supplied a selection voltage and the other a correction voltage. The. same arrangement was necessary for the groups of matrices for the vertical selection of rows and in addition two potentiometers. were required for each of the matrices.

The present; invention contemplates a circuit of simple design for receiving binary signals from a plurality of leads and converting these signals to voltages suitable for controlling cathode. raytubes of the character-forming type.

Accordingly, it is a primary object of this invention to provide an; improved control circuit for a character display tube.

Another object; of this-invention is to provide an imatent O 2,889,547v Patented June 2, 1959 proved circuit for receiving binary signals and translating them into corresponding voltages of equal increments.

Another object of the present invention is to provide a control circuit for character display tubes which is of simple design and certain in operation.

These and other objects of the invention will become apparent from the following description taken with the drawings in which:

Fig. l is a block diagram showing the elements of a character-forming cathode ray tube and the control circuits therefor;

Fig. 2 is a simplified schematic diagram of the character selector of the present invention; and

Fig. 3 is a schematic representation of the character selector and amplifier.

Before considering the control circuit of the present invention the character-forming cathode ray tube will be briefly described. This type of tube is diagrammatically represented in Fig. l and includes a glass envelope within which the elements are enclosed. A writing gun 11 is located at the end of the neck of the tube and serves to emit a stream of electrons similarly to the conventional cathode ray tube. A matrix 12 located in the path of the electron beam determines the character that is formed on the screen 10. The matrix acts as a stencil in that it forms the electron beam into selected characters as the beam passes therethrough. The matrix is divided into a plurality of rows and columns of characters so that the character formed by the electron beam will depend upon the point or location of the matrix at which the beam passes therethrough. It is seen therefore that by selectively deflecting the electron beam, any desired character represented on the matrix may be formed on the screen. This selective deflection of the beam is accomplished by a pair of vertical selection plates 13 and a pair of horizontal selection plates 9 interposed between the Writinggun and matrix. By applying predetermined potentials to the selection plates the desired. characters will be formed. and appear on the screen.

In order to prevent divergence of the electron. beam and insure that it passes between position deflection. plates 14 and. 15, a convergence coil 16 is provided. In addition to causing the beam to converge, the action of the coil also results in a 98 rotationv of the beam. To compensate. for this the matrix-is rotated. andthe vertical and. horizontal deflection plates are physically interchanged. The position deflection plates 14 and 15 serve to position the selected character in its proper location on the viewing screen. In order tosequentially locate the characters in columns and rows on the screen a staircase Wave form. of voltage is applied to each pair of deflection plates 14 and 15 as illustrated in Fig. 1. The number of steps per cycle of this waveform, which will be herein termed the format signal, will depend upon the number of horizontal rows and vertical columns desired. For example, if it is desired to display four rows of type each having sixteen characters, the format signal applied to the horizontal plates will have sixteen steps, and the vertical format signal will step once for each sixteen steps of the horizontal signal. Thus sixteen characters will be successively shifted horizontally without any vertical deflection and they will therefore appear in one horizontal line on the screen. A vertical step will then occur to start the next line for the following sixteen characters. Each vertical step has a time duration equal to sixteen horizontal steps.

In addition to the format signal, each pair of position deflection plates 14 and 15 has a correction signal applied thereto. The format signal above described is cyclic and would serve to correctly position the characters on the screen if the electron beam traversed the same path at all times in passing through the position deflection plates. However, it is readily seen that the path of the beam will, be dilferent foreach character since the characters have different relative positions on the matrix. Hence a correction voltage must be applied to the position deflection plates to compensate for the relative positions of the characters on the matrix. The correction voltage applied to the vertical position deflection plates 15will be different for each row on the matrix and the correction voltage to the horizontal plates 14 will be determined by the matrix column of the selected character. With the matrix character position thus compensated for by the correction signalsfthe format signals will trace through the characters to their proper positions on the viewing screen.

The function of the flood gun 17, found in certain character-forming cathode ray tubes, will not be considered since it is not necessary for a proper understanding of the present invention. It is sufiicient here to state that this gun functions in cooperationwith a pair of grids 7 and 8 located at the face of the tube.

Contrast grid 8 is of dielectric material that emits secondary electrons, and grid 7 serves as a collector grid, the potential of which may be varied to either store or erase characters.

' In the character selection system for which the present invention is designed, binary signals are obtained from a magnetic storage device 18 of the general type shown in Patent No. 2,540,654. For vertical selection the binary signals from the storage device appear on three leads 21, 22 and 23 and are passed to a character selector and amplifier 24 which will be described in detail hereinafter. The character selector converts the binary combinations of signals to selection voltages which are amplified and applied to the vertical selection plates 13. In addition, a correcting signal which is also a function of the received combinations of binary signals will be developed and passed by conductor 25 to the vertical position amplifier 26. Vertical format generator 27 produces the staircase wave form above described which is also passed to the vertical position amplifer. This amplifier will bring the correction signal and format signal to the proper levels and apply them to the vertical position deflection plates 15.

Considering now the signals as they are received from the magnetic storage device and appear on leads 21, 22 and 23, it is understood that they comprise an on or ofi condition on each of these leads. For convenience of description, an off condition will be termed zero and an on condition one (1). Since vertical selection is controlled by the signals on leads 21, 22, 23, the combination of zeros and ones thereon will determine the row on which the character will appear on the screen. For example, the following combinations of binary signals would result in selection of rows as follows:

Lead 23 Lead 22 Lead 21 Row ages and correction voltages are generally of even increments. For example, typical voltages for common character-forming cathode ray tubes are as follows:

Row Selection Correction voltage voltage 0 0 21 43 42 86 63 129 Etc. Etc.

Thus, in order to translate the received combinations of binary signals into proper character rows, it is necessary to convert these signals into voltages of even increments. The manner in which the character selector of the present invention performs this function will now be described by reference to Fig. 2 which serves to illustrate one basic concept of this'invention. The binary signals applied to leads 21, 22 and 23 may for the purposes of illustration be -7 volts for the zero condition and 0 volts for the 1 condition. These combinations of signals will result in a control voltage developing at point 28 which will be a function of the binary signals. For example, for the 011 signal which is the condition of 0 volts applied to leads 21 and 22 and -71 volts on lead 23, the control voltage at junction 28 may be calculated in the following manner. The resistance between junction 28 and the 0 volt potential is the parallel combination of R and R/2, or

Similarly, the control voltage at junction 28 can be calculated for the other binary combinations with the following results:

Signals on leads Control potent volts It is seen then that the binary signals are converted to analog voltages of equal increments by the resistors R, R/2 and R/4. The value of R may be any convenient resistance but it is necessary that the three resistors have relative values forming a geometric progression such as R, one-half R and one-quarter R. The control voltages obtained at junction 28 are then passed to the selection amplifier and to the vertical position amplifier as a correction signal which amplify the voltages to the proper levels depending upon the characteristics of the tube;

Reference will now be made to Fig. 3 which represents in detail the character selector and amplifier shown in block form in Fig. l. The binary input leads 21, 22 and 23 connect to selector resistors R, R and R respectively through input resistors 29. As described above, the resistance of R may be of any practical value but R must have a value of one-half R and R a value of one-quarter R to form a geometric progression. The other end of the selector resistors are joined at junction 28 and connected to the grid of'vacuum tube 31 which serves as the first stage of the selector amplifier. The cathode of tube 31 is grounded through cathode resistor 32 and the output is passed to the grid of vacuum tube 33 through a parallel combination of resistor 34 and capacitor 35. Negative battery connects to the cathode of tube 31 through an adjustable resistor 36 and to the grid of tube 33 through a fixed resistor 37. The output at the anode of tube 33 is, fed to, the'grid; of; tube 38 connected as a cathode follower. A resistor 39 connects the cathodes of tubes 31 and 38. Thus the control voltages developed at junction 28 are amplified to propervalues, and appear as selection signals at the cathode of tube 38. The correction signals are tapped off the cathode resistors 41 and 42 as shown. In order to stabilize the binary input signals, a clamping circuit is provided. This circuit takes the form of a pair of diodes connected to the junction of each selector resistor R, R and R and its respective input resistor 29. Selector resistor R has a pair of diodes 43 and 44 poled as shown in Fig. 3. One diode of each pair connects to ground and the other of each pair connect together and to the cathode of tube 45 over wire 46. The anode of tube 45 connects to positive battery and the cathode to negative battery through resistor 47. The grid of tube 45 is connected to the center tap of a potentiometer 48, one end of which is grounded and the other end connected to the negative battery through resistor 49. Tube 45 with its associated resistors and voltage potentials, serves as a source of low impedance clamp voltage adjustable in value for equalizing the voltage condition on leads 21, 22 and 23.

The selection signals derived at the cathode of tube 38 are applied directly to the vertical selection plates 13 as shown in Fig. 1. The correction signals are fed by wire to the vertical position amplifier 26 where they are combined with the staircase wave form from the format generator 27, amplified to the proper levels and applied to the vertical position plates 15. The details of the vertical format generator 27 and amplifier 26 may be of any known design and since the specific circuits of these elements form no part of the present invention, they are herein represented in block form.

The above description has been made by reference to the vertical selection, correction and positioning only of the cathode ray tube. Horizontal control of the tube is eflected in the same manner by binary signals from three additional input leads 51, 52 and 53. These binary signals are fed to a character selector and amplifier 54 which is similar to that shown in Fig. 3. Selection signals are derived and applied to the horizontal selection plates 9 and correction signals are passed to the horizontal position amplifier 56 over wire 55. These correction signals are combined with another staircase wave form from the horizontal format generator 57, amplified and applied to horizontal position plates 14.

Although the present invention has been described with reference to a specific embodiment thereof, it is understood that this is not to be considered as limiting the scope of the invention as defined by the appended claims.

What is claimed is:

l. A system for controlling a character forming cathode ray tube of the type having an electron beam source, a pair of vertical and horizontal selection plates, a character forming matrix, a pair of vertical and horizontal position deflection plates and a viewing screen upon which characters formed by said electron beam are visually represented, said system comprising a source of combinations of binary signals representing intelligence characters, vertical selector means and horizontal selector means each connected to the source of binary signals, means whereby each of said vertical selector means and said horizontal selector means develop a selection signal and a correction signal, the magnitude of each of said correction signals being a function of the associated selection signal, means coupling said vertical selector to said pair of vertical selection plates, means coupling said horizontal selector to said pair of horizontal selection plates, means to connect said correction signal developed in said vertical selector means to said pair of vertical position deflection plates, means to connect said correction signal developed in said horizontal selector means to said pair of horizontal position deflection plates, whereby selected characters are selectively positioned on the viewing screen, said vertical selector and said horizontal selector each comprising a plurality of resistor elements, one end of each of said elements adapted to have said binary signals applied thereto, the other end of said resistor elements being electrically connected to form a common junction, the resistance values of said elements forming a geometric progression having a progression factor of two whereby voltages of equal. increments are developed at said common junction in accordance with the binary signals applied to said resistance elements.

2. A system for controlling a character forming cathode ray tube of the type having an electron beam source, a pair of vertical and horizontal selection plates, a character forming matrix, a pair of vertical and horizontal position deflection plates and a viewing screen upon which characters formed by said electron beam are visually represented, said system comprising a source of combinations of binary signals representing intelligence characters, vertical selector means and horizontal selector means each connected to the source of binary signals, means whereby each of said vertical selector means and said horizontal selector means develop a selection signal and a correction signal, the magnitude of each of said correction signals being a function of the associated selection signal, means coupling said vertical selector to said pair of vertical selection plates, means coupling said horizontal selector to said pair of horizontal selection plates, means to connect said correction signal developed in said vertical selector means to said pair of vertical position deflection plates, means to connect said correction signal developed in said horizontal selector means to said pair of horizontal position deflection plates, whereby selected characters are selectively positioned on the viewing screen, said vertical selector and said horizontal selector each comprising a plurality of resistor elements, one end of each of said elements adapted to have said binary signals applied thereto, the other end of said resistor elements being electrically connected to form a common junction, the resistance values of said elements forming a geometric progression whereby voltages of equal increments are developed at said common junction in accordance with the binary signals applied to said resistance elements, a horizontal for-mat generator adapted to provide a staircase wave form, a vertical format generator adapted to provide a staircase wave form, means to connect said horizontal format generator to said horizontal position deflection plates, and means to connect said vertical format generator to said vertical position deflection plates whereby said characters sequentially appear in lines and columns on said viewing screen.

3. In a system of the character described wherein a source of binary signals control a character display device, said device including an electron beam source, means to deflect said beam, means whereby characters are formed by said beam in accordance with the deflection thereof, a viewing screen and positioning means whereby selected characters are sequentially positioned on the screen in lines and columns, control means connected to said means to deflect and to the source of binary signals, said control means comprising a plurality of resistance elements each joined at one end thereof to a common junction point, the values of said resistance elements forming a geometric progression whereby control voltages of equal increments are developed at the common junction point in accord- 'ance with the. combinations of received binary signals, means providing a positioning signal, said last named means including means to generate a signal having a staircase wave form, means providing a correction signal having a magnitude proportional to said control voltage, and means tofapply said positioning signal to said positioning means to sequentially position the formed characters in lines and columns on the viewing screen.

4. In a system of the character described wherein a source of 'binary signals control a character display device, said device including an electron beam source, means to deflect said beam, means whereby characters are formed by said beam in accordance with the deflection thereof, a viewing screen and positioning means whereby selected characters are sequentially positioned on the screen in lines and columns, control means connected to said means to deflect and to the source of binary signals, said control means comprising a plurality of resistance elements each joined at one end thereof to a common junction point, the values of said resistance elements forming a geometric progression whereby control voltages of equal increments are developed at, the common junction point in accordance withthecombinations of received binary signals, means to apply a positioning signalto said positioning means to sequentially position the char: acters in lines and columns on the viewing screen, said positioningsignal comprising a staircase signal anda correction signal derived from said control means.

References Cited in the file of this patent UNTI'ED STATES PATENTS 

